Thickness gauge



Sep't. 5, 1944. H. P. KUEHN! THIGKNESS GAUGE Filed Jan. 19,v 1943 Fig.

.Invetorz Y' Hans F'. K uehni,

y His Attorney.

- Patented Sept. 5, 1944 THICKN ESS GAUGE Hans P. Kuehni, Schenectady, N. Y.,'assgn0r to General Electric Company, a. corporation of New York Application January 19, 1943, sei-iai No. 412,841

(c1. ris-16s) 1 Claim.

My invention relates to a gaugeior determining the thickness of magnetic sheet material and its object is to provide a reliable, nondestructive gauge for sheet magnetic material which may be made portable and used from one side of the sheet material being tested.

The features of my invention which are be- I lieved to be novel and patentable will be pointed out in the claims appended hereto, For a better understanding of my invention, reference is made in the following description to the accompanying drawing in which Fig. 1 represents a gauge circuit system embodying my invention where sheets of known and unknown thickness are compared by saturating both with electromagnets and comparing the magnetomotive force stored in the two by means of a ballistic galvanometer calibrated in terms of thickness. In Fig. 1 the magnetizing circuit and ballistic galvanometer circuits are provided with manual switches. Fig. 2 represents the same type ofr system as in Fig. 1

Now when the switch I I is closed, the yokes and sheets II) and II will be magnetized and the ampere turns and yoke sections should be sufficient to saturate the sheet sections. The yokes are similar and when thus energized, a certain amount of magnetic energy is stored in cach magnetic circuit. If the sheets i and II are of the same thickness, the `energy stored in the two except that the switches are automatically 'conness, and I I represents a sheet of similar material I magnetic circuits willbe equal. However, if sheet II is thickeror thinner than sheet I more or less energy will be stored in the magnetic circuit of which yoke I3 is a part. In order to measure the difference in the energy thus stored, I pro` vide secondary or pickup windings 20 and 2i on the two yokes. These windings are similar and are connected in series in bucking relation to aballistic galvanometer 22 through a switch 23. It is immaterial whether the primary windings It and I5 are Aconnected in reverse relation or the secondarywindingszli and 2i are connected in reversed relationto provide the diierential bucking arrangement.

Assuming now that switches ii and 23 are closed, the opening of switch i'iwill release the stored magnetic energy, and voltages corresponding to 'such released energy will be induced in the secondary windings 2U andl 2i, and the diierence between these voltages will be conveyed to instrument 22 and produce a deflection proportionaly to the dlierence in the magnetic energy stored in the two systems. The indication can be doubled y.by reversing the switch Il.

but of.unknown thickness and the apparatus isA lemployed to determine thethickness of sheet II. For similarly magnetizing-a section of each sheet,

I provide magnetic yokes I2 and I3 having direct current magnetizing coils I4 and I5. These coils are' adapted to be connected to a direct current sourceof supply I6 through a reversing switch I'i. An ammeter I8 maybe included in the circuit and a glow tube I9 is preferably connected I0 although exact matching of -the air gaps, if

any, is not critical because of the low amount oi.' magnetic energy storedtherein;

When the switch i'i is reversed in one direction, the pointer of the -galvanometer will be kicked in one direction and when reversed in the opposite direction, it will be kicked in the opposite direction a distance proportional to thedifference inthickness, if any, ofthe sheets I0 and I I, and by trial the relative direction of galvanomand in the saturated sheet sections.v

eter deflection, when II is thicker or thinner than the standard I0, may be ascertained. The

galvanometer may then Ibe calibrated in suitable thickness units or in percentage thickness of the standard. The energy stored in the magnetic circuits is that of the yokes, the air gaps, if any, Since that stored in the yokes and air gaps is made equal,

Vthe dierence' is that due to the diierence in thickness of the sheets I II and II.'

An important aspect of this invention -is that most sheet steel materials used in industry have very closely the same saturation point although the saturation curves below saturation may be quite different. This is true of the various silicon sheet steels. 0f course materials should be used at I6 and II which have the same or approximately the same saturation point, or allowance made therefor. It follows that materials of the same thickness but having materially different saturation points may be sorted by the apparatus. It will be evident that the wires leading to magnetic core structure I3 may be grouped into a iiexible cable so as tovbe carried about and moved relative to the remaining apparatus, or the entire apparatus maybe 'readily made in portable form.

In Fig. 2y I have provided automatic means for operating'the switching arrangement with a view to saving energy, quickness and proper sequence of operation, and preventing overheating of the energizing coils. Those parts which are similar to those of Fig. l are identied by similar reference characters. Four relay operated switches 24, 25, 26, and 2'I are shown which are normally biased to the positions shown and moved to the right when their operating coils are energized.y

The coil of switch 24 is energized through a push button 23. 'Ihe remaining switch operating coils 1 are energized through the contacts of a cam controller 30 driven by a motor 3|. The direction of rotation of the cams of the controller is indicated by the arrow opposite cam 36. Cams 32, 33, and 34 close the coils of switches 25, 21, and 26 respectively. Cam 35 controls a holding circuit for the energizing coil of switch 21, and cam 36 controls a holding circuit for the energizing coil of switch 24. During a thickness measuring operation the several cams operate their respective contacts in the order in which the cams are numbered.

With the apparatus in the position shown, a testing operation is initiated by closing push button switch 28. 'I'his closes switch 24 and energizes motor 3| which starts. A holding circuit for the coil of switch 24 is -thus established magnetic circuit, comprising magnetic yoke sections 4|.and 42 and the standard sample I6 and through switch 24 and the contacts of cam 36.

Motor 3| starts and closes the circuit ofthe operating coil of, switch 25 through the contacts operated by cam 32. C1osure`of switch 25 estab-v lishes its own holding circuit and energizes the primary windings I4 and I5 through switch 26.

in the position as shown. The contacts of cam 33 next close, energizing' the coil of switch 21 which closes'to connect galvanometer 22 to the secondary coils 20 vand 2|. Closure of switch 21' also closes its own holding circuit through the contacts opposite cam 35. The contacts of cam 34 next close, energizing the coil of switch 26 thereby reversing the direction of current flow through primary windings I4 and I6 and also establishing a holding circuit for switch 26. As switch 26 reverses, the galvanometer 22 is deflected in accordance with any difference in the thickness of plates I0 and I I. Cam 35 next opens its contacts, deenergizing the coil of switch 21 and this switch opens. Finally, cam 36 opens its' contacts, deenergizing the coil of switch 24 which opens, deenergizing the coils of switches 25 and'26 and motor 3|. The controller then stops in about'sthe position shown and with all switches in the position shown. The operator may then transfer the yoke I3 to the next sheet or part to be tested and repeat the testing operation by merely pushing button 26 momentarily and reading the galvanometer 22.

In Fig. 3 I have represented a modification of myfinvention wherethe testing ux is produced -by a permanentmagnet 31.' This magnet' the sheet II to be tested. With the magnet armature 31 in the position shown, flux from its north pole enters pole piece 39 and divides, part going up through the upper branch of yoke 4|, through test piece II, down through the upper branch of yoke 42 to pole piece 40back to the south pole of the magnet 31. The remainder of the flux follows the parallel path through the lower branches of yokes 4| and 42 across standard sample sheet I0. Magnet 31 should be of sufficient capacity and strength, after stabilized knockdown, to force suflicient flux-across thevair gap and through the fparallel magnetic circuits to saturate the sheet sections I6 and II. The air gap opposite the ends of the magnet 31 are made as small as practicable. The ux will divide between the two paths in relation to the thickness ratio of the sheet sections |0 and II, since the two flux paths are otherwise made identical. To obtain a double measurement of the diierence in the stored magnetic energy in the two magnet circuits, the magnet is made reversible and is provided with a handle 43 and a spring 44 to facilitate re-' versing. Positioning stops 45 and 46 are provided to stop the handle in the two reversing positions. To operate, the handle is swung counterclockwise from the position shown againstvstop 45. This tensions the spring 44. The handle is then released and the magnet reverses its position between the pole pieces 36 y connections, and switches, is especially suitable for portable Work. For example, it may become desirable to examine a steel smokestack or large -tank to see if the thickness of the sheet steel used is not becoming too thin due to rust or other cause. A workman can carry the thickness testing apparatus with him up a ladder, for example, and obtain a close approximation of the thickness of a steel smokestack at rvarious points from the outside. Where the sheet material to be examined has a curved surface, the contacting 'surfaces of the yoke portion maybe curved accordingly to obtain an approximate fit.

In accordance with the provisions of the patent statutes, I lhave described the principle of operation of my invention together with thev apparatus which I now consider to `represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only il- .lustrative and that the invention may be carried out by ,other means.

What I claim as new and desire to secure by Letters Patent 0f the United States, is:

Apparatus for testing sheet magnetic material comprising-a magnetizing structure having magnetic yoke sections forming two sets of pole pieces across which similar lengths of sheet magis pivotedat 36 at its centerV so as to be reversed betwefe pole pieces `36 and 46 of the parallel said yoke sections between bothb sets of pole pieces sumcient to cause saturation in such sheet v magnetic material, said parallel iiux paths being similar except for any diierence caused by dii'- ferences in such sheet material, said permanent magnet being pivoted between said yoke sections so as to be reversible to simultaneously reverse the direction of ilux in the two parallel flux paths, aA spring for rotating said permanent magnet in one direction in a reversing operation,

means for stopping rotation of said permanent.

magnet in yoke magnetizing position when so f. reversed, similar secondary windings on the 

